Cardiovascular changes during and after different LBNP levels in men.
BACKGROUND
This study quantifies hemodynamic and thoracic impedance (TI) changes with four levels of lower body negative pressure (LBNP) from -15 to -65 mm Hg in seven healthy men in supine position 20 min before (pre-LBNP), 30 min during, and 20 min after suction (post-LBNP) as well as without suction (LBNP-0, rest control).


RESULTS
LBNP > 15 mm Hg increased basic TI by up to 2.2 omega (+9.5%). TI-computed stroke volume index (SVI) continuously decreased with time up to -12%, -28%, -36%, and -40% at the end of LBNP-15, -35, -55, and -65. TI-computed cardiac index decreased most (-14%) at LBNP-15 and -35, resulting in a 19% increase of calculated total peripheral resistance index at those intensities. Mean arterial pressure (MAP) did not change in any systematic way with lower LBNP levels, but increased +4.7% and +7.4% at the end of LBNP-55 and -65, respectively. Heart rate remained unchanged at LBNP-15, but continuously increased to reach +22%, +42%, and +55% at the end of LBNP-35, -55, and -65. After finishing LBNP, heart rate fell to values below both pre-LBNP and rest control for > or = 5 min (post-LBNP bradycardia). SVI transiently returned to, and MAP increased above, pre-LBNP levels after suction.


CONCLUSIONS
In conclusion, different levels of lower body subatmospheric pressure produced quantitatively different time course and dose-response patterns and remained non-hypotensive up to -65 mm Hg suction. Further, heart rate was depressed after LBNP, while arterial BP and TI-computed total peripheral resistance exceeded pre-stimulus levels, indicating an altered cardiovascular state after 30 min of simulated orthostasis.
László
Z
Z
Department of Physiology, School of Medicine, Karl-Franzens University, Graz, Austria.
Rössler
A
A
Hinghofer-Szalkay
H G
HG
D000328:Adult; D001794:Blood Pressure; D001919:Bradycardia / Q000209:etiology* / Q000503:physiopathology*; D002307:Cardiography, Impedance; D018495:Fluid Shifts; D006339:Heart Rate; D006801:Humans; D008150:Lower Body Negative Pressure / Q000009:adverse effects* / Q000379:methods*; D008297:Male; D013318:Stroke Volume; D013396:Suction; D016683:Supine Position; D013997:Time Factors; D014655:Vascular Resistance